The present invention relates to a battery using an anode active material which includes at least one of tin (Sn) and silicon (Si) as an element.
The development of batteries with a higher energy density has been demanded according to the downsizing of electronic devices. As a battery which meets the demand, a lithium metal secondary battery using precipitation-dissolution reactions of lithium (Li) is cited. However, in the lithium metal secondary battery, during charge, lithium (Li) is deposited on an anode to form a dendrite, thereby lithium is inactivated, so there is an issue that the cycle life of the lithium metal secondary battery is short.
As a battery with an improved cycle life, a lithium-ion secondary battery is commercially available. In an anode of the lithium-ion secondary battery, an anode active material such as a graphite material using an intercalation reaction of lithium between graphite layers, or a carbonaceous material using an application of insertion and extraction of lithium in pores is used. Therefore, in the lithium-ion secondary battery, lithium is not deposited to form a dendrite, and its cycle life is longer. Moreover, the graphite material or the carbonaceous material is stable in air, so the lithium-ion secondary battery has a big advantage in industrial production.
However, an anode capacity by intercalation has an upper limit stipulated by the composition C6Li of a first stage graphite intercalation compound. Moreover, it is industrially difficult to control a minute pore structure of the carbonaceous material, and by controlling the minute pore structure, the specific gravity of the carbonaceous material declines, so using the carbonaceous material is not an effective means of improving the anode capacity per unit volume and by extension to a battery capacity per unit volume. It is known that some low-temperature fired carbonaceous materials exhibit an anode discharge capacity exceeding 1000 mAh/g; however, there is an issue that when the battery includes a metal oxide or the like as a cathode, discharge voltage declines, because the metal oxide has a large capacity at a noble potential of 0.8 V or more relative to lithium metal.
Because of these issues, it is considered that it is difficult for existing carbonaceous materials to meet demands for a longer operating time of electronic devices in future and a higher energy density of power sources. Therefore, an anode active material having a greater capability to insert and extract lithium is desired.
On the other hand, as an anode active material capable of achieving a higher capacity, a material to which a fact that some kinds of lithium alloys are electrochemically and reversibly produced and decomposed is applied has been widely researched. For example, a lithium-aluminum alloy has been widely researched, and in U.S. Pat. No. 4,950,566, a silicon alloy has been reported. However, when these alloys are used for an anode of a battery, cycle characteristics will decline. One of the reasons is that these alloys expand and shrink according to charge and discharge, thereby the alloys are pulverized every time charge and discharge are repeated
Therefore, in order to prevent the pulverization of such an alloy, for example, it is considered that an element not involved in expansion and shrinkage according to insertion and extraction of lithium is substituted for a part of the alloy. For example, LiSiaOb (0≦a, 0<b<2) (refer to Japanese Unexamined Patent Application publication No. H6-325765), LicSi1-dMdOe (where M is a metal element except for alkali metal or a metalloid element except for silicon; 0≦c; 0<d<1; and 0<e<2) (refer to Japanese Unexamined Patent Application Publication No. H7-230800), a lithium-aluminum-tellurium alloy (refer to Japanese Unexamined Patent Application Publication No. H7-288130) and the like have been proposed. Further, a compound including one or more kinds of non-metal elements and a Group 14 metal element or a Group 14 metalloid element in the long form of the periodic table of the elements (refer to Japanese Unexamined Patent Application Publication No. H 11-102705) has been proposed.
However, even if these anode active materials are used, a decline in cycle characteristics due to expansion and shrinkage is large, so there is an issue that they are not adequate to be used for a mobile devices putting emphasis on cycle characteristics. Moreover, the mobile devices are left under a high temperature environment in many cases, so the improvement of high temperature storage characteristics has been demanded.